Transient analysis of short, high-concentration, gain-clamped Er³⁺-Yb³⁺ codoped fiber amplifiers

A theoretical study of the dynamics of short high-concentration gain-clamped Er³⁺-Yb³⁺ codoped fiber amplifiers is presented. The effect of various parameters on the transient power excursions and relaxation oscillation frequency of a given signal input channel when other signal channels are added or dropped from an initial steady-state configuration is analyzed. In particular, the effects of Er³⁺ clustering, Yb³⁺ concentration, fiber length, lasing wavelength, pump wavelength, pump power, and cavity losses are shown. The numerical results demonstrate the importance of Yb³⁺ sensitization in achieving stable gain-clamped operation in a range of operating conditions. It is shown that the amplitude of power excursions is typically small, e.g., less than 0.1 dB, provided that the amount of Er³⁺ ions in the clusters is kept small.